Adjustable impedance, for example adjustable resistors



Dec. 15, 1953 J. ERKELENS 2,662,955

ADJUSTABLE IMPEDANCE, FOR EXAMPLE ADJUSTABLE RESISTORS Filed April 18, 1952 INVENTOR Johannes Erkelens AGE/VT Patented Dec. 15,1953

ADJUSTABLE IMPEDANCE, FOR EXAMPLE ADJUSTABLE RESISTORS Johannes Erkelens, Eindhoven, Netherlands, as-

signor to Hartford National Bank and Trust Company, Hartford, Conn, as trustee Application April 18, 1952, Serial No. 283,035

Claims priority, application Netherlands June 13, 1951 2 Claims. 1

This invention relates to an adjustable impedance for example an adjustable resistor constituted by an impedance body and an adjusting member which is capable of turning along it and which has secured to it a contact wire extending in accordance with a predetermined curve, said contact wire making contact with the impedance body at a point which is dependent upon the position of the adjusting member. Such apparatus are used for controlling determined magnitudes such, for example, as the temperature in a boiler which is required to vary in a predetermined manner in connection with a process to be followed. The adjusting memher, which may have the shape of a drum, is driven very slowly by means of an electric motor, a controlling magnitude being derived from the variation in resistance which, in the case mentioned above, controls the temperature for a certain period, for example a day, in the desired manner.

The object of the present invention is to provide a construction in which the contact wire may be secured to the surface of the adjusting member in accordance with the desired curve in a simple and easy manner.

Accordin to the invention, an adjustable impedance, for example an adjustable resistor, constituted by an impedance body and an adjusting member which is adapted to turn along it and which has secured to it a contact wire extending in accordance with a predetermined curve, said contact wire making contact with the impedance body at a point which is dependent upon the position of the adjusting member, is characterized in that the contact wire is secured to the surface of the adjusting member by means of conical pins which are axially split and which, with their thinner non-split extremities first, are introduced into holes of the adjusting member, the contact wire being clamped in the split extremities of the pins in such manner that the wire projects from the surface of the adjusting member at a greater extent than the pins. A circular contact wire, which has the same moment of inertia in any direction on account of its circular cross-section and hence is most suitable for the purpose, may thus readily be secured to the surface of the adjusting member.

The slit is preferably somewhat narrowed at the free extremities of the pins projecting from the surface of the adjusting member, so that the contact wire is completely enclosed between this narrow portion and the surface of the adjusting member.

In order that the invention may be readily carried into eiiect it will now be described in greater detail with reference to the accompanying drawing, by Way of example, in which Fig. 1 is a perspective view of on embodiment and the other figures illustrate the manner of securing the contact wire.

Figures 2, 2a, 3 and 4 are details of the slit pin ll.

Figures 5 and 5a are details of the auxiliary tool 2 I.

Figure 6 shows the auxiliary tool and the split pin.

The embodiment shown in Fig. 1 comprises an adjusting member in the form of a drum 4, to which a contact wire 3 is secured. The drum I is a tube of insulating material, for example, hard paper, and is adapted to turn about a metal shaft 5, which has connected to it one extremity of the wire 3. One end of the shaft 5 is engaged by a contact spring l, which is connected to a terminal 9.

An insulating supporting rod i i provided parallel to the shaft 5 has wound on it a helical winding It, for example of resistance wire, which engages the contact wire 3. The point on the rod H at which contact is established is dependent upon the adjustment of the drum I, so that the resistance is variable by this adjustment between one of the output terminals it of the wire winding l3 on the one hand and the terminal 9 on the other hand.

The contact wire 3 is secured to the surface of the drum l with the use of conical split pins I1, which are introduced into radial holes of the drum i. The Figures 2 to 6 inclusive show the shape of said pins and the manner of securing the contact wire. As may be seen from the figures, the slit in the pins i! extends through a length of several times the maximum diameter of the contact wire 3. After a hole which is somewhat too small has been drilled into the wall of the drum l, the pin ll, as shown in Fig. 2, is driven approximately halfway into the hole with the use of an auxiliary tool in the form of a plate [9. Subsequently (see Fig. 3) the wire 3 is laid in the slit of the pin I! and the pin is driven farther into the drum i by means of a hammer. Owing to the conical shape of the pin, the wire 3 is thus clamped in position and, as shown in Fig. 4, the slit is slightly narrowed at the free extremity projecting from the drum I due to a burr being formed. Subsequently, the pin 11 is driven into the wall of the drum l with the use of an auxiliary tool 2| shown in Fig. 5

' to secure the contact wire 3 to the surface of the drum l in accordance with any arbitrary curve. For this purpose the curve preliminarily.

drawn on the surface of the drum I, at regular intervals holes being drilled along the curve into which the pins ii are introduced in the manner illustrated in Fig. 2. It may thus readily 'be ensured with the use of the plate It that the slit in the pin extends in the direction of the tangent to the curve. The hole and the crosssection of the pin are required to :be of a shape such that it remains possible for the pin to be turned, within the hole. The wire 3 may be bent into the desired shape corresponding to the curve preliminarily drawn either before or during inserting the wire into the slits .of the pins ii, the shape being retained when the pins are driven in.

A contact wire of circular cross-section is :best suited to the purpose aimed .at .on account of its uniform flexibility in any direction. As will be evident from the foregoing, the circular shape creates no difiiculty in obtaining reliable attachment of the wire.

In contradistinction to the foregoing, the adjusting member, .instead of having theshape-oi a drum, may be aifiat, rotatable disc, on which the contact wire in the form of a fiat spiral is provided. If desired, the adjusting member may have the shape of .a strip and may be slidable instead of rotatable. The impedance :body may naturally be a helically-wound inductance coil instead of a resistor. When use is made of a resistor, it may be constituted by a rod of poorly conductive material instead of a winding of wire.

Instead of securing the conical pins I? in the tubular drum I by hammering, the securing may alternatively be eiiected by providing the pins with screw-thread having screwed on it, inside the drum l, a nut which draws the pin into the drum as far as necessary.

What I claim is: l. A variable resistor comprising an insulated supporting rod, a helical winding on said supporting rod, a movable adjusting member being provided with a plurality of holes therein disposed in a predetermined curved path, said member being positioned adjacent to said supporting rod, a contact wire for engaging said helical winding at a plurality of separate points on said winding depending upon the position of said adjustable member, means for securing said contact wire on said adjusting member along the curvilinear line formed by said curved path, said means comprising a plurality of pins in said holes, said pins being tapered and split axially in the larger ends thereof, the larger ends of said pins being adapted to be wedged in said holes with said contact wire being clamped in the split ends of said pins substantially perpendicular thereto so that a portion of the peripheral surface of said contact wire projects beyond the larger ends of said pins and forms said predetermined curved path.

2. A variable resistor comprising an insulated supporting rod, a helical winding on said supporting rod, a cylindrical drum with a plurality of radial holes therein disposed in a predetermined curved path and being positioned adjacent to said supporting rod, a contact wire for engaging said helical winding at a plurality of separate points on said winding depending upon the position of said adjustable member, means for securing said contact wire on said adjusting member along the curvilinear line formed by said curved path, said means comprising a plurality of pins positioned radially in said holes, said pins being tapered and split axially in the larger ends thereof, the larger ends of said pins'being adapted to be wedged in said holes with said contact wire being clamped in the split ends of said pins substantially perpendicular thereto so that a portion of the peripheral surface of said contact wire projects beyond the larger ends of said .pins and forms said predetermined curved path.

J OHANNES ERKELENS.

References Cited in the file of this patent -UWITED STATES PATENTS Number 

